Sweden, as well as the adjacent country Norway, has a high concentration of petroglyphs (ristningar or hällristningar in Swedish) throughout the country, with the highest concentration in the province of Bohuslän. The earliest images can, however, be found in the province of Jämtland, dating from 5000 BC. They depict wild animals such as elk, reindeer, bears and seals. The period 2300–500 BC was the most intensive carving period, with carvings of agriculture, warfare, ships, domesticated animals, etc. Also, petroglyphs with themes of sexual nature have been found in Bohuslän; these are dated from 800–500 BC.
The conversion from pre-Christian beliefs to Christianity was a complex, gradual, and at times possibly violent (see Temple at Uppsala) process. The main early source of religious influence was England due to interactions between Scandinavians and Saxons in the Danelaw, and Irish missionary monks. The German influence was less obvious in the beginning (despite an early missionary attempt by Ansgar), but gradually emerged as the dominant religious force in the area (especially after the Norman conquest of England). Despite the close relations between Swedish and Russian aristocracy (see also Rus'), there is no direct evidence of Orthodox influence, possibly because of language barriers.
This consolidated state of Sweden already included Finland presumably from an early crusade into the area of Tavastland in central current day Finland.
After the Black Death and internal power struggles in Sweden, Queen Margaret I of Denmark united the Nordic countries in the Kalmar Union in 1397, with the approval of the Swedish nobility. Continual tension of economic nature within the countries and within the union gradually led to open conflict between the Swedes and the Danes in the 15th century, however. The union's final disintegration in the early 16th century brought on a long-lived rivalry between Denmark on one side and Sweden on the other.
In the 16th century, Gustav Vasa fought for an independent Sweden, crushing an attempt to restore the Kalmar Union and laying the foundation for modern Sweden. At the same time, he broke with the Roman Catholic Church and established the Reformation.
After winning wars against Denmark-Norway, Russia, and Poland during the 17th century, Sweden emerged as a Great Power, despite having scarcely more than 1 million inhabitants. Its contributions during the Thirty Years' War under Gustavus Adolphus helped determine the political, as well as the religious, balance of power in Europe.
By the treaties of Brömsebro, 1645, and Roskilde, 1658, Sweden acquired important provinces of Denmark and Norway. Following the Peace of Westphalia in 1648, Sweden ruled Ingria, in which Saint Petersburg later would be founded, Estonia, Livonia, and important coastal towns and other areas of northern Germany.
Russia, Saxony-Poland, and Denmark-Norway pooled their power in 1700 and attacked the Swedish empire. Although the young Swedish King Charles XII won spectacular victories in the early years of the Great Northern War, his plan to attack Moscow and force Russia into peace proved too ambitious; he was shot during the siege of Frederiksten fortress in Norway in 1718. In the subsequent peace treaties, the allied powers, joined by Prussia and by England-Hanover, ended Sweden's reign as a great power and introduced a period of limited monarchy under parliamentary rule.
Following half a century of parliamentary domination came the reaction. A bloodless coup d'état perpetrated by King Gustav III brought back absolute monarchy, a state of affairs that would last until involvement in the Napoleonic wars forced Sweden to cede Finland to Russia in 1809.
The following year, the Swedish King's adopted heir, French Marshal Jean-Baptiste Bernadotte, was elected Crown Prince Charles by the Riksdag. In 1813, his forces joined the allies against Napoleon. In the Treaty of Kiel, the king of Denmark-Norway ceded mainland Norway to the Swedish king. Norway, however, declared its independence, adopted a constitution and chose a new king. Sweden invaded Norway to enforce the terms of the Kiel treaty. After a short war, the peace of Moss established a personal union between the two states. The union lasted until 1905, when it was peacefully dissolved at Norway's request.
Sweden's predominantly agricultural economy shifted gradually from village to private farm-based agriculture during the Industrial Revolution, but this change failed to bring economic and social improvements commensurate with the rate of population growth. About 1 million Swedes emigrated to the United States between 1850 and 1890. The 19th century was marked by the emergence of a liberal opposition press, the abolition of guild monopolies in trade and manufacturing in favour of free enterprise, the introduction of taxation and voting reforms, the installation of national military service, and the rise in the electorate of three major party groups – Social Democrat, Liberal, and Conservative.
During and after World War I, in which Sweden remained neutral, the country benefitted from the world-wide demand for Swedish steel, ball bearings, wood pulp, and matches. Post-war prosperity provided the foundations for the social welfare policies characteristic of modern Sweden. Foreign policy concerns in the 1930s centered on Soviet and German expansionism, which stimulated abortive efforts at Nordic defence co-operation. Sweden followed a policy of armed neutrality during World War II and currently remains non-aligned.
By the 1970s the economies of the rest of western Europe, particularly that of West Germany, had been restored and the Swedish economy, now containing a large tax funded public sector, stagnated. In 1976, the social democrats lost their majority. The 1976 parliamentary elections brought a liberal/right-wing coalition to power. Over the next six years, four governments ruled and fell, composed by all or some of the parties that had won in 1976. The fourth liberal government in these years came under fire by Social Democrats & trade unions and the Moderate Party, culminating in the Social Democrats regaining power in 1982.
In the early 1960’s U.S. nuclear submarines armed with mid-range nuclear missiles of type Polaris A-1 were deployed outside the Swedish west coast. Range and safety considerations made this a good area from which to launch a retaliatory nuclear strike on Moscow. The submarines had to be very close to the Swedish coast to hit their intended targets though. As a consequence of this, in 1960, the same year that the submarines were first deployed, the U.S. provided Sweden with a military security guarantee. The U.S. promised to provide military force in aid of Sweden in case of Soviet aggression. Knowledge of this guarantee was by the Swedish governments kept from the Swedish public until 1994, when a Swedish research commission found evidence for it.
As part of the military cooperation the U.S. provided much help in the development of the Saab 37 Viggen, as a strong Swedish air force was seen as necessary to keep Soviet anti-submarine aircraft from operating in the missile launch area. In return Swedish scientists at the Royal Institute of Technology made considerable contributions to enhancing the targeting performance of the Polaris missiles.
On February 28 1986, the social democratic leader and Swedish prime minister Olof Palme was murdered, after which many people felt Sweden had "lost its innocence". In the beginning of the 1990s there occurred once again an economic crisis with high unemployment and many banks and companies going bankrupt. Sweden became a member of the European Union in 1995, after which the country more and more has started to stray from its post-war and cold war neutrality. In a referendum held in 2003, the majority of the population voted against the adoption of the Euro as the country's official currency.